1. Field
An embodiment of the present invention relates to a reformer with high durability.
2. Description of Related Art
In recent years due to concern about environmental pollution, various alternative and less polluting energy sources, such as fuel cells with relatively high energy efficiency have been developed.
A fuel cell is a device (or a type of energy source) that directly converts chemical energy into electric energy through electrochemical reaction of hydrogen and oxygen. A fuel cell is classified as a polyelectrolyte fuel cell, a solid oxide fuel cell, or a molten carbonate fuel cell depending on the type of its electrolyte. Hydrogen used in the polyelectrolyte fuel cell is typically acquired from reformate that has been reformed from hydrocarbon fuel such as methanol, liquid petroleum gas (LPG), gasoline, etc. This reforming process is necessary because of the difficulties in storing and transporting pure hydrogen. The reformate may be a steam-type reformate resulting from a steam reform reaction of the hydrocarbon fuel. Here, in most fuel cell systems using the steam reform type reformate, a heating unit is required to supply heat for the steam reform reaction.
In the reforming process, after electrons are generated from a stack, reformate and other remaining materials are discharged from an anode of the stack, and this discharge is referred to as anode off gas (AOG). In the related art, the AOG is combusted by using an additional catalytic combustor and/or mixed with atmospheric gas to decrease the concentration of other discharge gases such as H2, CO, and CH4 in the AOG.
However, as worldwide environmental standards grow, there is a desire and need to more positively manage the AOG in the manufacturing of a fuel cell that may be used in an indoor environment. Also, considering that one of the main components of the AOG gas is hydrogen (H2), and to satisfy environmental concerns of atmospheric pollution, there is an urgent desire or need to technologically develop a method for combusting the AOG gas that allows for both processing of the AOG and for improving the efficiency of the reformer.
To this end, an embodiment of the present invention provides a reformer that oxidizes or combusts the AOG by returning the AOG to a heating unit of the reformer to improve thermal efficiency and to satisfy certain environmental concerns. However, due to oxidation of the reformate, oxidation of the heating unit fuel, and/or oxidation of the AOG, the reformer has characteristic high-temperature atmosphere, that generates a plurality of hot spots. As such, there is a need to develop a design that can alleviate or distribute these hot spots. That is, in order to allow the reformer to operate for a long time without deterioration or damage, as described above, thermal shock caused by repetition of thermal expansion and shrinkage should be reduced or minimized through the alleviation or distribution of the hot spots to thereby reduce or minimize the deterioration and damage caused due to thermal stresses on the reformer.
However, because the heating unit operates at a high-temperature atmosphere, it may be difficult for a method to distribute and alleviate the hot spots to be satisfactory for the management of the lifespan of the reformer. As such, a more positive protection structure is needed and desired.